1. Field of the Invention
The present invention generally relates to cylindrical vibration isolating bushings each comprising an elastic body and being applicable to suspension bushings, engine roll mounts, and member mounts for use in automotive vehicles, and other mounts or bushings for use in various devices or equipments other than the automotive vehicles, such as mounts for supporting electric mortars, for example. More particularly, the present invention is concerned with a vibration isolating bushing that is novel in construction and that is capable of establishing a satisfactory ratio of spring constants of the elastic body in two mutually orthogonal diametric vibration input directions, without needing a provision of slits or voids located on a diametric line extending in at least one of the two vibration input directions, which may cause noises upon application of a relatively large vibrational load in the vibration input direction.
2. Description of the Related Art
Vibration isolating bushings are known as one type of vibration damping devices to be installed between two members of a vibration-transmitting system. JP-A-5-126185 discloses a known example of such vibration isolating bushings, wherein an outer sleeve member is disposed radially outward of an inner shaft member with a radial spacing therebetween, and is elastically connected with the inner shaft member by means of a cylindrical elastic body disposed in the radial spacing between the inner shaft member and the outer sleeve member. Such a vibration isolating bushing is capable of exhibiting a vibration isolating effect with respect to vibrational loads applied in a variety of diametric or radial directions, an axial direction, a torsional direction, a twisting direction and other possible directions. For this capability, the vibration isolating bushings have been used for suspension bushings for use in automotive vehicles, for example.
In order to mutually adjust spring constants of the elastic body in two mutually orthogonal diametric directions, or alternatively to adjust the spring constant of the elastic body in a twisting direction, the cylindrical elastic body of the vibration isolating bushing is generally provided with axial slits extending therethrough in the axial direction with a given circumferential width. The axial slits are formed to be located on a diametric line extending along at least one of the two vibration input directions, as seen in a transverse cross section of the vibration isolating bushing.
However, when a relatively large vibrational load is applied to the vibration isolating bushing in the diametric line of the vibration input direction, radially opposed parts of an inner surface of each slit are brought into abutting contact and rub together in a direction in which these parts of the inner surface are displaced relative to each other. As a result, the conventional vibration isolating bushing is prone to cause noises and fine vibrations due to the contact and rub between the radially opposed parts of the inner surface of the slit.